Game prototyping has become a common practice in game design. Existing prototyping studies focused on the core mechanics, the level design, interface and so on. The rise of online multiplayer gaming has make in-game social engagement and interaction becoming an increasingly important component of game mechanism. However, a systematic research methods focusing on the influences of in-game social rules and mechanisms to a player group have not yet formed. We propose an approach of ABM (multi-agent simulation) method to study in-game social interaction, by establishing a simulation environment including the player’s agent and the rules of in-game interaction. By implementing ABM approach, the social interaction outcomes could be tested independent from other aspects of game design.